1. Field of the Invention
The present invention relates to a common-rail-type fuel injection device having two separate common rails for supplying high-pressure fuel to an internal combustion engine.
2. Description of Related Art
A common-rail-type fuel injection device having two separate common rails is often used for an internal combustion engine having two cylinder lines, such as a V-type engine or a parallel-facing-type engine. This type of fuel injection device is described, e.g., in an article entitled “Der erste Achtzylinder-Dieselmotor mit Direkteinspritzung von BMW” (authors: Ferenc Anisits, Klaus B. Borgmann, Helmut Kratochwill and Fritz Steinparzer) in “Motortechnische Zeitschrift (MTZ)” issued in 1999. A relevant portion of the injection device is shown in FIG. 5 attached hereto.
In this fuel injection device, high-pressure fuel is supplied from a fuel supply pump J1 to a distributing block J2, and then the high-pressure fuel is distributed to a first common rail J3 and to a second common rail J4. The high-pressure fuel is injected into cylinders of a first block from each injector J5 connected to the first common rail J3. Similarly, the high-pressure fuel is injected into cylinders of a second block from each injector J6 connected to the second common rail J4. The distributing block J2 functions to distribute the high-pressure fuel to two common rails separately disposed.
It is conceivable to eliminate the distributing block J2 and to connect the first common rail J3 and the second common rail J4 in series. In this arrangement, the high-pressure fuel is directly supplied to the first common rail J3 from the fuel supply pump J1 and then to the second common rail J4 from the first common rail J3. If this arrangement successfully works, the distributing block J2 can be eliminated and the device is simplified as a whole. However, pressure waves are generated between the first common rail J3 and the second common rail J4 by connecting both common rails with a connecting passage. The pressure waves are caused by a pulsating pressure in the fuel supply pump J1 and fuel injection from the injectors J5, J6. A pressure difference between two common rails J3 and J4 is caused by the influence of the pressure waves. Therefore, a problem that an injection pressure differs between the first group of injectors J5 and the second group of injectors J6 occurs. The injection pressure difference results in a difference in an injection amount.